The present invention relates generally to fluid handling systems, and more particularly provides an improved liquified gas pumping and vaporization system which may be utilized to efficiently convert a cryogenic fluid, such as liquid nitrogen, to a gas for injection into subterranean formations for the enhancement of hydrocarbon deposit recovery therefrom, or for other uses.
In the art of liquified gas pumping systems, several proposals have been made for a system wherein a liquified gas, such as liquid nitrogen, is pumped to a predetermined discharge pressure and then vaporized for use in a variety of applications such as injection into subterranean formations for the recovery of hydrocarbon deposits. Examples of previously proposed pumping and vaporization systems of this general type are described in U.S. Pat. No. 3,229,472 to Beers and U.S. Pat. No. 4,197,712 to Zwick et al. Various other conventional nitrogen pumping and vaporization systems are exemplified in U.S. Pat. No. 4,409,927 to Loesch et al, U.S. Pat. No. 4,290,271 to Granger, and U.S. Pat. No. 4,226,605 to Van Don.
Liquified gas pumping and vaporization systems of this general type typically utilize an internal combustion engine as the main power source for driving both a process fluid pump and a coolant fluid pump. Heat generated by the driving engine is transferred to a coolant fluid flow circuit and then transferred from the coolant to the process fluid to heat and vaporize it.
One disadvantage with conventional systems is the relative complexity of the engine coolant flow circuit and the lack of reasonably precise control over the amount of heat generated for transfer to the liquid to be vaporized. Although both the Beers and Zwick et al patents suggest utilizing engine coolant as a source of heat for vaporizing a cryogenic fluid such as liquid nitrogen, Beers suggests that the drive engine be artifically loaded by a hydraulic braking device and that the heat generated in the braking device be exchanged between a hydraulic fluid and the engine coolant. This type of arrangement for artificially loading the engine for both control of liquified gas pump output and the heat generated by the braking device to heat the process fluid is relatively inefficient and results in the requirement that excess heat be rejected from the system. Stated in another manner, more heat is generated than is required by the system, and the resulting excess heat must be simply dissipated to atmosphere. Additionally, the heat generated by the artificial load device (i.e., the hydraulic braking device) cannot be directly transferred to the coolant - it must be indirectly transferred to the coolant via a separate heat exchanger. This results in a further heating inefficiency in the system.
The Zwick et al patent discloses several variations of a nitrogen pumping and vaporization system in which a back pressure device is interposed in either the hydraulic circuit, the coolant circuit, or in the process fluid circuit portion of the system in a manner such that the artificial engine load imposed by the back pressure device is made directly proportional to the flow rate of the nitrogen through the system. To maintain an automatic proportionality between the total engine heat added to the coolant and the flow rate of the nitrogen, the loading back pressure must ordinarily be set at a level corresponding to the minimum process fluid back pressure likely to be encountered during operation of the system. Stated otherwise, the artificial back pressure load must be set to completely vaporize the flowing nitrogen, and bring it to a predetermined constant discharge temperature, for the maximum nitrogen flow rate likely to be encountered. Because of this operational scheme in the Zwick et al system, a considerable amount of coolant heat must normally be rejected from the system, and cannot be used to vaporize the flowing nitrogen, during normal operating conditions of the system.
Another problem presented by conventional liquid pumping and vaporization systems arises from the connection of the driving engine's coolant jacket in series with the coolant flow circuit such that during normal periods of system operation all of the coolant fluid flows through the coolant jacket of the engine. When the temperature of the coolant exceeds a predetermined level, the engine's radiator functions in a conventional manner to protect the engine from overheating.
This connection of the engine in series with the system's coolant flow circuit effectively limits the minimum temperature of the coolant flowing therethrough to approximately 160.degree.. Such coolant temperature limitation significantly increases the required size of various heat exchangers utilized in the system, and therefore can significantly increase the construction cost of the system.
Yet another problem encountered in conventional systems of this general type is the difficulty in precisely controlling the temperature of coolant fluid flowing through the coolant flow circuit. Because of the coolant fluid flow circuitry utilized in such conventional systems, a rather wide fluctuation in coolant temperature is frequently encountered.
It can be seen from the foregoing that a variety of problems, limitations, and disadvantages are present in conventional cryogenic fluid pumping and vaporization systems. It is accordingly an object of the present invention to provide an improved system which eliminates or minimizes above-mentioned and other problems, limitations and disadvantages associated with systems of this type.